1. Field of the Invention
The present invention pertains to data transmission systems generally, and in particular to transmission systems for time-slot-oriented data.
2. Discussion of the Related Art
A transmission system for transmitting time-slot-oriented data between an exchange termination and a line termination is usually part of a communication system having a switching facility and subscriber line facilities. The subscriber line facilities have subscriber interfaces for connecting communication terminals to the communication system.
According to the ITU-T G.960 Standard, the subscriber line facilities are connected to the switching facility of the communication system via a line termination and an exchange termination. Such a communication system is used for setting up and, respectively, clearing down narrow-band communication connections between communication terminals connected to the subscriber line facilities and to provide for narrow-band communication—for example voice or data communication—between the communication terminals.
In modern communication systems, data transmission between the exchange termination and the line termination usually takes place on the basis of the time-slot-oriented data format IOM-2 (ISDN Oriented Modular Interface) formed from a periodic sequence of channel-individual information segments—called time-division multiplex channel in the text which follows. As a rule, one time-division multiplex channel is in each case allocated to each subscriber interface of a subscriber line facility in this arrangement.
In modern communication engineering, there is a need for broadband transmission of information such as, for example, still and moving pictures in videophone applications or of large volumes of data in the Internet. This increases the significance of transmission techniques for high and variable data transmission rates (greater than 100 Mbit/s) which take into account both the requirements of the data transmission (high speed at variable transmission bit rate) and the requirements of voice data transmission (maintaining time correlations with a data transmission via a network) so that the separate networks currently existing for the various purposes can be integrated in one network. A known data transmission method for high data speeds is the so-called Asynchronous Transfer Mode (ATM). Data transmission on the basis of the Asynchronous Transfer Mode currently enables a variable transmission bit rate of up to 622 Mbit/s to be obtained.
In the cell-based data transmission method known as Asynchronous Transfer Mode (ATM), so-called ATM cells are used for transporting fixed-length data packets. An ATM cell is composed of a so-called “header” with a length of five bytes which contains switching data relevant to the transportation of an ATM cell, and a so-called “payload” with a length of 48 bytes.
Data transmission via an ATM-based network generally takes place in so-called virtual paths or virtual channels. For this purpose, interconnection tables with switching information consisting of a virtual channel identifier and of a virtual path identifier are set up in the respective ATM network nodes of the ATM-based network by an exchange of signaling information during a connection set-up before the beginning of the actual user data transmission. In the interconnection tables, a so-called VCI value is assigned to the virtual channel identifier and a so-called VPI value is assigned to the virtual path identifier.
The switching information entered in the interconnection table of an ATM network node establishes how the virtual paths or, respectively, virtual channels contained in the virtual paths of the incoming and outgoing connections at the ATM network node are correlated with one another by the signaling, that is to say which input is connected to which output by a switching. ATM cells transmitted via these virtual connections (virtual paths and virtual channels) have switching data essentially consisting of a VPI value and a VCI value in the header. The ATM header data are processed, i.e. the switching data arranged therein are detected and evaluated at the input of an ATM network node. The ATM cells are then switched through by the ATM network node to an output of the ATM network node representing a certain destination by means of the switching information stored in the interconnection table.
German Offenlegungsschrift DE 196 04 244 A1, shows a transmission system between an exchange termination and a line termination in which transmission is implemented via an ATM-based network. In this arrangement, subscriber interfaces for connecting ISDN (Integrated Services Digital Network) oriented communication terminals by ATM hubs connected to the ATM-based network are provided. The exchange termination of the communication system and the line termination implemented by the ATM hub have an ATM interface unit via which, on the one hand, a connection to the ATM-based network is implemented and, on the other hand, the IOM-2 data format usually provided for a data transmission between the exchange termination and the line termination is converted to the ATM-based data format. Or, the ATM-based data format is converted to the IOM-2 data format.
For addressing a subscriber interface of the ATM hub via the ATM-based network, a permanently set up ATM channel of the ATM-based network is allocated to each time-division multiplex channel of the IOM-2 data format, i.e. an unambiguous VPI/VCI address is allocated to each subscriber interface of an ATM hub for a data transmission via the ATM-based network. The VPI-VCI addresses are allocated to the respective subscriber interfaces and managed manually in the switching system.
If a fault occurs at a subscriber interface or at a communication terminal connected to the subscriber interface, only the VPI/VCI address of the defective subscriber interface or of the communication terminal connected to the subscriber interface is known in the switching system. It is not possible to find the ATM hub associated with the communication terminal.
A method for finding the association of a communication terminal with a subscriber interface of an ATM hub which is already used is the tracing back of the path in the ATM-based network starting from the switching system to the communication terminal, i.e. determining the path in the ATM-based network by means of the switching information stored in the ATM network nodes. In most cases, however, this is not possible since the operator of the ATM-based network is not, as a rule, the operator of the telecommunication network implemented on this. The switching information stored in the ATM network nodes is thus not available to the operator of the telecommunication network.
Thus, according to the terminology of the ITU-T G.960 Standard (3/93) “access digital section for ISDN basic rate access”, especially pages 2 and 3, the present invention is based on data transmission occurring at the V reference point.